4.3BSD DEC DMZ effective transfer rate lacking?

[idallen at watcgl.waterloo.edu]

From: "Ian! D. Allen [CGL]" <idallen>

When I "cat file" through a DEC DMZ-32 port, I don't get the character rate
I thought I would get.  I get about 14000 bps when the port is set to
19200 bps and about 7200 bps when the port is set to 9600 bps.  The rates
through our DEC DMF-32 are almost identical to (indeed, slightly faster
than) the expected port bit rate, so I know our unloaded VAX 8600 running
4.3 BSD can keep up.

What is going on?  It is a known problem that these DEC DMZ devices don't
perform at their assigned rates?